1. Field of the Invention
The invention relates to a high-pressure injection system, in particular for auto-igniting internal combustion engines.
2. Description of the Prior Art
European Patent Disclosure EP 0 711 914 A1 relates to a pressure-controlled fuel injection system, in which, with the aid of a high-pressure pump, fuel is compressed to a first high fuel pressure of approximately 1200 bar and stored in a first pressure reservoir. The fuel under high pressure is also supplied to a second pressure reservoir, in which, by regulation of its fuel delivery by means of a 2/2-way valve, a second high fuel pressure of approximately 400 bar is maintained. Via a valve control unit, either the lower or the higher fuel pressure is conducted into the nozzle chamber of an injector. There, a spring-loaded valve body is lifted from its valve seat by the pressure, so that fuel can emerge from the nozzle opening into the combustion chamber.
A disadvantage of this known fuel injection system is the fact that all the fuel must first be compressed to the higher pressure level and then some of the fuel is relieved again to the lower pressure level. Moreover, the high-pressure pump, since it is driven by the camshaft of the engine, is constantly in operation, even when the desired pressure in the respective pressure reservoir has already been built up. This permanent generation of high pressure and the ensuing relief to the low-pressure level stand in the way of improved efficiency.
The high-pressure fuel pumps used in the field of self-igniting internal combustion engines are currently capable of building up pressures of up to approximately 2200 bar. Pressures beyond that are possible either with two-stage high-pressure pumps or with additional pressure boosters outside or inside the fuel injectors. Two-stage high-pressure pumps require markedly greater installation space and are not compatible with current systems. Moreover, the mechanical load in terms of pump development is considered critical. Internal and external pressure boosters are currently used solely as local pressure boosters for individual injectors; that is, per injector, one pressure booster is in use. In terms of expense, this first means a large number of additional components, and in terms of function, it means poor efficiency in pressure-boosted injection of small quantities, since for each pressure boosting event, there must be a minimum turnover in the control quantity in the pressure booster. One such central pressure booster is known for instance from European Patent Disclosure EP 1 125 046 B1.